Treatment of hypereutectoid steel



Oct. 8, 1957 J. FIELD TREATMENT OF HYPEREUTECTOID STEEL Filed Feb. 11, 1955 INVENTOR ATTORNEY United States Patent TREATMENT or HYTEREUTECTOID STEEL Joseph Field, Bethlehem, Pa., assignor to Bethlehem Steel Company, a corporation of Pennsylvania Application February 11, 1955, Serial No. 487,652

6 Claims. (Cl. 75-129) My invention relates to an improved process for treating hypereutectoid highly alloyed steel, to produce a steel, particularly tool steel, having improved properties and characteristics. By highly alloyed steel is meant a steel having a total alloy content of more than 8.00% of carbide forming elements.

It has long been required by users of steel tools, particularly high speed tools having free carbides in their structure, that such tools be relatively free of carbide segregates so that the cutting edge of the tools will be free of brittle carbide groupings often associated with early failure.

The production of steel of this type has in the past been very costly, because in the freezing of ingots the natural solidification process occurs, in which as freezing progresses inwardly from the ingot mold walls the liquid portion becomes increasingly richer in carbon and alloying elements, with the result that the undesirable compleX carbide segregates migrate to the center portion of the ingot. These segregates also tend to be concentrated in the upper portion of the ingot.

The principal factors which have been found in the past, to affect the carbide distribution are (l) casting temperature (the lower the temperature the less segregation), and (2) ingot mold design (the faster the freezing rate the less segregation). However, even though these factors are controlled by practical production methods, only a relatively small portion of the ingot will meet the rigid requirements of many of the high speed steel users.

It is an object of my invention to provide a process for treating hypereutectoid highly alloyed steels, particularly high speed steels, which will impart to such steels a relatively uniform distribution of carbides, thus permitting the utilization of a much greater percentage of the ingot.

Other objects and advantages of the invention will become apparent from the following description taken with the drawings, in which Fig. 1 is a photolithograph of a thin section of an ingot of high speed steel taken longitudinally through the center of the ingot showing the heavy carbide segregation resulting from the practice of the best of prior art processes;

Fig. 2 is a view similar to Fig. 1, showing the improved distribution of carbides resulting from treatment of molten high speed steel in the ladle according to my invention; and

Fig. 3 is a view similar to Fig. 1, showing the improved distribution of carbides resulting from treatment of molten high speed steel in the ingot mold according to my invention.

Generally speaking, the invention comprises the steps of establishing a bath of hypereutectoid highly alloyed 2,809,109 Patented Oct. 8, 1957 ice steel, and especially so-called high speed tool steels, for example, steels of the following analyses:

tapping said molten steel into a ladle, pouring said molten steel into an ingot mold, and adding to said molten steel an addition agent or compound containing Al Ti Zr Mn B Si Fe Percent Percent Percent Percent Percent Percent 10. 0-15. 0 15. 025. 0 3. 0-5. 0 6. 0-10. 0 35-. 65 3. 0-7. 0 Bal.

A preferred composition within this broad range which has been found particularly efiicacious contains Al. Ti Zr Mn B Si Fe 13.0 20.0 4.0 8.0 .5 5.0 Balance This compound may be added in the form of granules and is added to the steelin the ladle during tapping, or in the ingot mold while pouring. It has been found that from three to ten pounds of the compound per ton of steel, or in percentages .15% to .50%, will impart marked benefits to said steel. The ingots shown in the drawing were treated with 5 lbs. of compound per ton of steel, or .25%.

The benefits obtained by my novel treatment are well demonstrated by the drawings. These drawings are photolithographs showing thin sections of ingots which were cast, annealed, and cut longitudinally. These sections were of a thickness of .200" and included the metallurgical center of the ingot. The section was then X-rayed and radiographs were obtained. A positive print was made of the radiograph and a photograph taken of the print. The photolithographs were taken of the photograph. By this technique, the carbides are revealed as dark areas 1, while the porosity or open metal common to ingot structure shows as white areas 2. It can be seen that the untreated ingot representing the best of prior ait practices, Fig. 1, contains heavy carbide segregation which extends from the top of the ingot to approximately one half of the length of the ingot. In this case only the bottom half of the ingot would meet the rigid requirements of tool steel users.

In contradistinction to the standard ingot structure shown in Fig. 1, it is clearly shown in Figs. 2 and 3 how the treatment of the invention results in a structure having very little segregation of carbides. These two latter figures show a uniform high grade structure which makes it possible to use most of the ingot for tools of high quality.

It is believed that the addition of the compound used in the process of the invention prior to the start of solidification of the ingot provides nuclei for crystallization at widely separated points in the ingot so that the carbides are trapped in the solidifying steel, and prevented from migrating and segregating in the central portion of the ingot.

I claim:

1. A method for improving the properties of hypereutectoid steel having a total alloy content of more than 8.00% of carbide forming elements which comprises establishing a molten bath of said steel, tapping said steel into a ladle, pouring said steel into a mold, and adding to said steel after tapping and prior to solidification, from .15 to .50% of an addition agent containing about 10.0 to 15.0% aluminum, 15.0 to 25.0% titanium, 3.0 to 5.0% zirconium, 6.0 to 10.0% manganese, .35 to .65% boron, 3.0 to 7.0% silicon and the balance essentially iron.

2. A method for improving the properties of hypereutectoid steel having a total alloy content of more than 8.00% of carbide forming elements which comprises establishing a molten bath of said steel, tapping said steel into a ladle, pouring said steel into a mold, and adding to said steel in the ladle after tapping and prior to solidification, from .15 to .50% of an addition agent containing about 10.0 to 15.0% aluminum, 15.0 to 25.0% titanium, 3.0 to 5.0% zirconium, 6.0 to 10.0% manganese, .35 to .65% boron, 3.0 to 7.0% silicon and the balance essentially iron.

3. A method for improving the properties of hypereutectoid steel having a total alloy content of more than 8.00% of carbide forming elements which comprises establishing a molten bath of said steel, tapping said steel into a ladle, pouring said steel into a mold, and adding to said steel in the mold and prior to solidification, from .15% to 50% of an addition agent containing about 10.0 to 15.0% aluminum, 15.0% to 25.0% titanium, 3.0 to 5.0% zirconium, 6.0 to 10.0% manganese, .35 to .65% boron, 3.0 to 7.0% silicon and the balance essentially 1ron.

4. A method for improving the properties of-hypereutectoid steel having a totalalloy content of more than 8.00% of carbide forming elements which comprises establishing a molten bath of said steel, tapping said steel into a ladle, pouring said steel into a mold, and adding to said steel after tapping and prior to solidification, from .15% to of an addition agent containing about 10.0 to 15.0% aluminum, 15.0 to 25.0% titanium, 3.0 to 5.0% zirconium, 6.0 to 10.0% manganese, .35 to .65% boron, 3.0 to 7.0% silicon and the balance essentially iron, whereby a uniform distribution of carbides is imparted to said steel upon solidification.

5. A method for improving the properties of hypercutectoid high speed tool steel which comprises establishing a molten bath of said steel, tapping said steel into a ladle, pouring said steel into a mold, and adding to said steel after tapping and prior to solidification, from .15 to 50% of an addition agent containing about 10.0 to 15.0% aluminum, 15.0 to 25.0% titanium, 3.0 to 5.0% zirconium, 6.0 to 10.0% manganese, .35 to .65% boron, 3.0 to 7.0% silicon and the balance essentially iron, whereby a uniform distribution of carbides is imparted to said steel upon solidification.

6. A method for improving the properties of hypereutectoid steel having a total alloy content of more than 8.00% of carbide forming elements which comprises establishing a molten'bath of said steel, tapping said steel into a ladle, pouring said steel into a mold, and adding to said steel after tapping and prior to solidification, from .15% to .'50% of an addition agent containing about 13.0% aluminum, 20.0% titanium, 4.0% zirconium, 8.0% manganese, .5 boron, 5.0% silicon, and the balance essentially iron, whereby a uniform distribution of carbides is imparted to said steel upon solidification.

References Cited in the file of this patent Tool Steels, Gill et al., published by American Society for Metals, Cleveland, Ohio, pages 23-24, 521-522.

Metals Handbook, 1948 edition, page 340. Published by the American Society for Metals, Cleveland, Ohio. 

5. A METHOD FOR IMPROVING THE PROPERTIES OF HYPEREUTECTOID HIGH SPEED TOOL STEEL WHICHCOMPRISES ESTABLISHING A MOLTEN BATH OF SAID STEEL, TAPPING SAID STEEL INTO A LADLE, POURING SAID STEEL INTO A MOLD, ANDDADDING TO SAID STEEL AFTER TAPPING AND PRIOR TO SOLIDIFICATION, FROM .15% TO .50% OF AN ADDITION AGENT CONTAINING ABOUT 10.0 TO 15.0% ALUMINUM, 15.0 TO 25.0% TITANIUM, 3.0 TO 5.0% ZIRCONIUM, 6.0 TO 10.0% MANGANESE, .35 TO .65% BORON, 3.0 TO 7.0% SILICON AND THE BALANCE ESSENTIALLY IRON, WHEREBY A UNIFORM DISTRIBUTION OF CARBIDES IS IMPARTED TO SAID STEEL UPON SOLIDIFICATION. 